In Greek mythology Leto (Greek: Λητώ or Λατώ) is a daughter of the Titans Coeus and Phoebe, the sister of Asteria.

The island of Kos is claimed as her birthplace. In the Olympian scheme,  Zeus is the father of her twins, Apollo and Artemis, the Letoides, which Leto conceived after her hidden beauty accidentally caught the eyes of Zeus. Classical Greek myths record little about Leto other than her pregnancy and her search for a place where she could give birth to Apollo and Artemis, since Hera in her jealousy caused all lands to shun her. Finally, she found an island that was not attached to the ocean floor so it was not considered land and she could give birth. This is her only active mythic role: once Apollo and Artemis are grown, Leto withdraws, to remain a dim and benevolent matronly figure upon Olympus. In Roman mythology, Leto's Roman equivalent is Latona, a Latinization of her name, influenced by Etruscan Letun.

In Crete, at the city of DrerosSpyridon Marinatos uncovered an eighth-century post-Minoan hearth house temple in which there were found three unique figures of Apollo, Artemis and Leto made of brass sheeting hammered over a shaped core (sphyrelata). Walter Burkert notes that in Phaistos she appears in connection with an initiation cult.

Leto was identified from the fourth century onwards with the principal local mother goddess of Anatolian Lycia, as the region became Hellenized. In Greek inscriptions, the Letoides are referred to as the "national gods" of the country. Her sanctuary, the Letoon near Xanthos predated Hellenic influence in the region, however, and united the Lycian confederacy of city-states. The Hellenes of Kos also claimed Leto as their own. Another sanctuary, more recently identified, was at Oenoanda in the north of Lycia. There was a further Letoon at Delos.

Leto's primal nature may be deduced from the natures of her father and mother, who may have been Titans of the sun and moon. Citation needed Her Titan father is called "Coeus", and though H. J. Rose considers his name and nature uncertain, he is in one Roman source given the name Polus, which may relate him to the sphere of heaven from pole to pole. The name of Leto's mother, "Phoebe" (Φοίβη "pure, bright"), is identical to the epithet of her son Apollo, Φοῖβος Ἀπόλλων, throughout Homer.